1. Field of the Invention
This invention relates to improvements in an electrophotographic member which employs amorphous silicon as a photoconductive material.
2. Description of the Prior Art
As photoconductive materials to be used for electrophotographic members, there have heretofore been inorganic substances such as Se, CdS and ZnO and organic substances such as poly-N-vinyl carbazole (PVK) and trinitrofluorenone (TNF). They exhibit high photoconductivities. However, in case of forming photoconductive layers by using these materials as they are or by dispersing the powders thereof in binders of organic substances, there has been the disadvantage that the layers exhibit insufficient hardnesses, so they have their surfaces flawed or wear away during the operations as the electrophotographic members. In addition, many of these materials are substances harmful to the human body. It is therefore unfavorable that the layers wear away to adhere on copying paper even if in small amounts. In order to improve these disadvantages, it has been proposed to employ amorphous silicon for the photoconductive layer (Japanese Laid-open Patent Application No. 54-78135). The amorphous silicon layer is higher in hardness than the aforecited conventional photoconductive layers and is scarcely toxic, so that the disadvantages of the conventional photoconductive layers are improved. The amorphous silicon layer, however, exhibits a resistivity in dark which is too low for the electrophotographic member. The amorphous silicon layer having a high resistivity on the order of 10 .sup.10 .OMEGA..multidot.cm exhibits a gain being too low, and only an unsatisfactory one is obtained as the electrophotographic member. In order to overcome this disadvantage, there has been proposed a layer structure wherein at least two sorts of amorphous silicon layers having different conductivity types such as the n-type, n.sup.+ -type, p-type, p.sup.+ -type and i-type are formed into a junction and wherein photo-carriers are generated in a depletion layer formed in the junction part (Japanese Laid-open Patent Application No. 54-121743). However, in case where the depletion layer is formed by putting the two or more layers of the different conductivity types into the junction in this way, it is difficult to form the depletion layer in the surface of the photoconductive layer. Therefore, the important surface part of the photoconductive layer which must hold a charge pattern exhibits a low resistivity to give rise to the lateral flow of the charge pattern. It is consequently feared that the resolution of electrophotography will degrade.